Previous results from our laboratory have provided a method for subclassification of Haemophilus influenzae type b (Hib) based on heterogeneity in the outer membrane proteins (OMP) of different isolates. We propose next to investigate the role of OMP and lipopolysaccharide (LPS) in immunity to this organism. OMP and lipopolysaccharide will be purified from different strains of Hib and characterized using chemical and immunologic methods. The purified derivatives will then be used to develop sensitive and specific serologic techniques for measurement of antibody. Rabbit antiserum will be prepared to purified proteins, and to various LPS preparations, and tested for in vitro bactericidal activity, and for protection against Hib infection in infant rats. The immunogenicity of the different components of the outer membrane will also be examined in humans by measurement of antibody concentrations in serum samples obtained during and after invasive Hib infections. The results of these studies should help determine whether OMP or LPS constituents might be useful for incorporation in an Haemophilus influenzae type b vaccine.